1. Field of the Invention
The present invention relates generally to an internal combustion engine having a lean NOx catalyst and, more particularly, to an internal combustion engine having a lean NOx catalyst which is provided in an exhaust system of the internal combustion engine in which the atmospheric air in the exhaust system becomes especially an oxygen excessive state, for purging nitrogen oxide contained in an exhaust gas in this exhaust system by use of a reducing agent.
2. Description of the Prior Art
For example, an occlusive reduction type lean NOx catalyst may be exemplified as a catalyst used in an internal combustion engine such as a gasoline direct injection lean-burn engine, a diesel engine and the like exhibiting a high thermal efficiency in which the atmospheric air in an exhaust system is in an oxygen excessive state while quantities of hydrocarbon and carbon monoxide are small.
The occlusive reduction type lean NOx catalyst may be classified as an intermittent processing type lean NOx catalyst for temporarily occluding the nitrogen oxide to the catalyst in the lean atmospheric air, and promptly reducing and purging the nitrogen oxide occluded by supplying a proper amount of reducing agent to the catalyst in the reduction atmospheric air afterward.
Note that there is a selective reduction type lean NOx catalyst other than the occlusive reduction type lean NOx catalyst.
The selective reduction type lean NOx catalyst is categorized as a consecutive processing type lean NOx catalyst for consecutively selectively reducing and purging the nitrogen oxide by supplying the reducing agent to the catalyst. Further, the hydrocarbon may be exemplified as the reducing agent as disclosed in, e.g., Japanese Patent Application Laid-Open Publication No. 6-117225. Carbon monoxide in addition to the hydrocarbon is also known as the reducing agent.
When the hydrocarbon is used as the reducing agent, the hydrocarbon is partially oxidated to generate active species. Then, the active species react to the nitrogen oxide and reduce it, thereby generating nitrogen, water and carbon dioxide which are not harmful to the human body.
Then, according to the above-mentioned Publication, an engine fuel injection device normally used in the internal combustion engine, such as an injector, for the supply of fuel at a compression stroke, is also used for supplying the reducing agent by injection at expansion stroke through exhaust stroke. Of these injections, the former injection for driving the engine is termed a main injection, while the latter injection is called a sub-injection.
Further, activation of the lean NOx catalyst is needed for making the lean NOx catalyst function effectively. For activating the lean NOx catalyst, the lean NOx catalyst must be warmed up to above an activation temperature enough to function effectively. Then, according to the conventional technology, the catalyst temperature is raised to the activation temperature or higher by utilizing the heat of an exhaust gas emitted by the internal combustion engine.
The sub-injection is, as described above, conducted at the expansion stroke through exhaust stoke, and is therefore effected at a point of time when the piston moves more downward than a top dead center.
It is preferable in terms of performing the combustion that the fuel is injected when the piston is in the vicinity of the top dead center. Then, for attaining this, the fuel injection device is installed at a fixed injection angle. Therefore, the fuel is hard to vaporize in such a sub-injection that the fuel is injected when the piston is at a point lower than the top dead center of the stroke thereof. It might be therefore presumed that the as-liquefied fuel could be supplied as the reducing agent to the lean NOx catalyst.
It is more preferable for effectively utilizing the fuel as the reducing agent to vaporize the fuel than to liquefy the fuel. It is, however, difficult to well catch a timing for executing the sub-injection so as to vaporize the fuel in the fuel injection device such as the injector of which the original function is to inject the combustion-oriented fuel for driving the engine. Hence, there is desired a technology capable of supplying the as-vaporized reducing agent to the lean NOx catalyst without effecting the sub-injection.
According to the conventional technology, the lean NOx catalyst effectively functions after starting up the engine, at which time the Lean NOx catalyst can reach the activation temperature or higher. The lean NOx catalyst can not be warmed up to above the activation temperature in a stop state before starting up the engine.
Further, even after the start-up of the engine, it takes a considerable length of time till the lean NOx catalyst is activated, and during such period of time the lean NOx catalyst does not effectively function. Besides, in the internal combustion engine such as the direct injection engine and the diesel engine exhibiting the high thermal efficiency, when the internal combustion engine is in an operation state such as, e.g., in a light-load region, an exhaust temperature at that time is low, and hence the heat enough to activate the lean NOx catalyst is not transferred throughout the exhaust system due to the low exhaust temperature. Consequently, it might occur that the lean NOx catalyst is rather cooled by the low-temperature exhaust gas of the internal combustion engine, for example, during a deceleration after the acceleration.
Then, it becomes difficult to perform a recovery from so-called SOx-poisoning and a recovery from SOF(Soluble Organic Fraction)-poisoning of the lean NOx catalyst, and besides it is also difficult to remove particulate matters. Note that poisonings by sulfur without being limited to the SOx-poisoning are generically termed S-poisoning. Further, as known well, the SOF-poisoning is not defined as the poisoning caused by sulfur and does not therefore come under the category of the S-poisoning.
On the other hand, if an external load is applied to the internal combustion engine by executing intake/exhaust throttling operations in order to enrich the atmospheric air in the exhaust system with a rise in the exhaust temperature, this might in turn cause a deteriorated fuel consumption and lead to a production of particulate matters.
Further, though not disclosed in the above-mentioned Publication, the internal combustion engine is provided with a combustion heater of such a type as to effect the air suction from the atmospheric air in order to enhance a car room warming performance and an engine warp-up performance in some cases. The combustion gas emitted from the combustion heater is discharged to an exhaust passageway, and it can be considered that the lean NOx catalyst provided in the exhaust passageway is thereby activated. In that case, however, in a state where the internal combustion engine is driven, an exhaust pressure in the internal combustion engine is higher than an exhaust pressure in the combustion heater. Therefore, the combustion gas from the combustion heater can not be discharged to the exhaust passageway. Hence, it is impossible to effectively utilize the heat of the combustion gas from the combustion heater for warming up the lean NOx catalyst. Further, because of a differential pressure between the exhaust pressure in the internal combustion engine and the exhaust pressure in the combustion heater, it might occur that the engine exhaust gas flows back to the combustion heater via a combustion gas discharge passageway for discharging the combustion gas from the combustion heater to outside. Note that the combustion gas from the combustion heater and the exhaust gas emitted by the internal combustion engine are hereinafter simply called the combustion gas and the exhaust gas, respectively, unless otherwise specified.
It is a primary object of the present invention, which was devised under such circumstances to obviate the above problems, to provide an internal combustion engine having a lean NOx catalyst, which can provide the effects, for example, as described below.
{circle around (1+L )} Capable of sufficiently supplying the lean NOx catalyst with a reducing agent such as hydrocarbon even by eliminating the necessity of a sub-injection.
{circle around (2+L )} Sufficiently raising a temperature in the exhaust system from before starting up the engine so that the lean NOx catalyst provided in the exhaust system of the internal combustion engine functions effectively with the start of the internal combustion engine.
{circle around (3+L )} Well performing purification of the exhaust gas, recovery from S-poisoning or SOF-poisoning of the lean NOx catalyst and removal of particulate matters.
{circle around (4+L )} Restraining production of the particulate matters.
{circle around (5+L )} Speeding up activation of the lean NOx catalyst by allowing the combustion gas through the exhaust passageway according to the necessity while preventing a back flow to the combustion heater even after the start-up of the engine.
To accomplish the above object, an internal combustion engine having a lean NOx catalyst according to the present invention adopts the following constructions.
According to a first aspect of the present invention, an internal combustion engine having a lean NOx catalyst, comprises a combustion heater for raising temperatures of engine related elements, a lean NOx catalyst provided in an engine exhaust passageway for purifying an engine exhaust gas, and a combustion gas introducing passageway for introducing a combustion gas emitted by the combustion heater, toward upstream of the lean NOx catalyst in the engine exhaust passageway when a request for a reproducing process of the lean NOx catalyst is made.
Herein, xe2x80x9cthe engine related elementsxe2x80x9d imply elements of the internal combustion engine itself such as engine cooling water, a cylinder block, a cylinder head and the like.
xe2x80x9cThe enginexe2x80x9d given herein may include internal combustion engines such as not only a typical port injection gasoline engine but also a gasoline direct injection lean-burn engine and a diesel engine or a CNG (Compressed Natural Gas) engine.
xe2x80x9cThe combustion heaterxe2x80x9d is preferably attached to the internal combustion engine as a separate member from the internal combustion engine body. It is because the combustion of the heater is conducted independently without being influenced at all by the combustion within cylinders of the internal combustion engine body, and, if the combustion gas emitted at that time can be discharged to the engine exhaust system, the combustion gas can be utilized for increasing a temperature in the engine exhaust system and for executing catalyst processing even before starting up the engine.
xe2x80x9cThe lean NOx catalystxe2x80x9d may be the occlusive reduction type lean NOx catalyst or the selective reduction type lean NOx catalyst.
xe2x80x9cThe combustion gasxe2x80x9d may preferably contain, as its component, hydrocarbon and carbon monoxide as the necessity may arise. It is therefore preferable that fuels for the internal combustion engine such as a gasoline and a light oil are used as fuels for combustion in the combustion heater. This is because the gasoline and the like produce an unburned gas if not completely burned, and the unburned gas contains the hydrocarbon and the carbon monoxide serving as reducing agents.
xe2x80x9cThe combustion gas introducing passagewayxe2x80x9d is a passageway used only for warming the lean NOx catalyst without permitting the heat to escape during passing of the combustion gas through this passageway, and it is preferable that the combustion gas introducing passageway is a passageway for guiding the combustion gas to the exhaust system while by passing the cylinders of the internal combustion engine. Note that the heat of the combustion gas will hereinafter be called combustion gas heat, unless otherwise specified.
In the internal combustion engine having the lean NOx catalyst according to the present invention, when the request for the reproducing process of the lean NOx catalyst is made, the combustion gas flows toward the upstream-side of the lean NOx catalyst via the combustion gas introducing passageway. Accordingly, if the combustion gas heat at that time is high, the temperature of the lean NOx catalyst is increased by the high-heat combustion gas having arrived there and is thereby activated irrespective of the operating or non-operating of the internal combustion engine.
Besides, if a state of the combustion in the combustion heater is adjusted so that the combustion gas contains proper quantities of hydrocarbon and carbon monoxide, it is feasible to ensure the hydrocarbon and the carbon monoxide serving as the reducing agents enough to purify the exhaust gas and effect the reduction of the lean NOx catalyst and recovery from the S-poisoning without, requiring the sub-injection which has hitherto been used. Accordingly, if the combustion heater has been operated from the time when the engine was in the stop state, the exhaust gas can be, as a matter of course, purified effectively immediately after starting up the internal combustion engine, and there can be also amply expected the reduction of the lean NOx catalyst and the recovery from the S-poisoning thereof.
Further, when the combustion heater is used for the purpose of raising the temperature in the exhaust system in order to activate the catalyst, the external load may not be applied to the internal combustion engine unlike the prior art, and consequently there must be a less amount of unburned gas produced. Therefore, the particulate matters can be restrained from being produced. Then, even if the SOF-poisoning occurs in the lean NOx catalyst or the particulate matters adhered thereto, the soluble organic fractions (SOF) and the particulate matters can be burned by increasing the combustion gas heat, and it is therefore feasible to make the recovery from the SOF-poisoning of the lean NOx catalyst and remove the particulate matters.
According to a second aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the first aspect, the time when making the request for the reproducing process of the lean NOx catalyst is at least one of the times of a time when requiring a NOx reduction of the lean NOx catalyst, a time when requiring recovery from S-poisoning of the lean NOx catalyst or recovery from SOF-poisoning thereof, and a time when requiring removal of particulate matters from the lean NOx catalyst.
According to a third aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the first aspect, the combustion gas introducing passageway may also be an EGR (Exhaust Gas Recirculation) passageway. Note that the EGR passageway essentially serves to re-circulate the exhaust gas of the internal combustion engine from an exhaust passageway to an intake passageway in order to flow some proportion of the exhaust gas back to an intake system for lowering generation of NOx.
In the internal combustion engine having the lean NOx catalyst according to the present invention, the EGR passageway, if applied as the combustion gas introducing passageway when the engine stops, is defined as an existing structure in the internal combustion engine, and hence there is no necessity for newly providing the combustion gas introducing passageway. With this structure, the whole apparatus does not become complicated in configuration, and besides the costs can be reduced.
According to a fourth aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the first aspect, the combustion gas introducing passageway may be a bypass passageway extending to a point anterior to the lean NOx catalyst in the engine exhaust passageway and bypassing the engine body.
In the internal combustion engine having the lean NOx catalyst according to the present invention, the combustion gas emitted from the combustion heater can be flowed directly to the point anterior to the catalyst converter, i.e., in close proximity to the lean NOx catalyst via the bypass passageway. Therefore, the combustion gas heat can be utilized effectively without any waste for activating the lean NOx catalyst. Further, if the combustion gas introducing passageway is structured as an heat insulated passageway, the combustion gas heat can be utilized solely for warming the catalyst by preventing the heat held by the combustion gas from escaping somewhere during the passing of the combustion gas through the combustion gas introducing passageway. Consequently, the lean NOx catalyst can be warmed further effectively. Accordingly, the exhaust gas can be purified much sooner corresponding thereto, and it is feasible to make the NOx reduction of the lean NOx catalyst and the recovery from the S-poisoning or SOF-poisoning from the lean NOx catalyst, and to remove the particulate matters. That is, the lean NOx catalyst can be reproduced preferably by setting the temperature of the lean NOx catalyst so as to become suitable for the recoveries from the above poisonings and the removable of the particulate matters.
According to a fifth aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the second aspect, wherein when requiring the NOx reduction of the lean NOx catalyst, and when requiring the recovery from the S-poisoning of the lean NOx catalyst, an air-fuel ratio of the combustion gas may be enriched as in the case of the lean NOx catalyst being in the reduction atmospheric air. The reduction atmospheric air connoted herein is the atmospheric air containing large quantities of hydrocarbon and carbon monoxide serving as the reducing agents for the lean NOx catalyst.
In the internal combustion engine having the lean NOx catalyst according to the present invention, when increasing a quantity of fuel supply to the combustion heater, the air-fuel ratio of the combustion gas becomes rich, and the combustion gas heat rises. Besides, the exhaust gas comes to contain a greater amount of reduction gas components such as the hydrocarbon and the carbon monoxide. Hence, it is possible to make the NOx reduction of the lean NOx catalyst and recovery from the S-poisoning thereof.
According to a sixth aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the first aspect, wherein when a differential pressure between a pressure of an engine intake system and a pressure of an engine exhaust system is at a predetermined value or larger, the combustion gas emitted from the combustion heater may be flowed to the combustion gas introducing passageway. Note that xe2x80x9cthe predetermined valuexe2x80x9d is a value with which the pressure of the engine intake system is higher than the pressure of the engine exhaust system when operating the combustion heater in the state where the above differential pressure is over the predetermined value, and hence the combustion gas from the combustion heater is allowed to flow toward the engine exhaust system, i.e., a value with which a back flow does not occur.
According to a seventh aspect of the invention, the internal combustion engine having the lean NOx catalyst according to the first aspect, may further comprise a supercharger, wherein when the pressure of the engine intake system becomes equal to or above the predetermined value by dint of supercharging of the supercharger, the combustion gas emitted from the combustion heater is flowed to the combustion gas introducing passageway. xe2x80x9cThe predetermined valuexe2x80x9d in this case, is substantially the same as the predetermined value according to the sixth aspect of the invention. Namely, this is a value with which the pressure of the engine intake system is higher than the pressure of the engine exhaust system when operating the combustion heater in the state where the pressure in the engine intake system is equal to or above the predetermined value, and hence the combustion gas from the combustion heater is allowed to flow toward the engine exhaust system, i.e., a value with which a back flow does not occur.
In the internal combustion engine having the lean NOx catalyst according to the present invention, the internal combustion engine is provided with the supercharger, e.g., a turbo charger, and the pressure in the intake system is raised higher by operating a compressor thereof than an exhaust pressure at a point, anterior to the lean NOx catalyst, of the exhaust passageway, to which to the combustion gas is introduced. With this structure, the high-heat combustion gas can be supplied in bypass to the lean NOx catalyst via the combustion gas introducing passageway.
Hence, in the case of the internal combustion engine provided with no turbo charger, even when executing such an engine operation that the pressure in the exhaust system becomes higher than the pressure in the intake system, and if the internal combustion engine comes under such an engine having the supercharger, in particular, the turbo charger as in the case of the present invention, the intake system pressure is raised higher than the exhaust system pressure by operating the compressor. Therefore, the high-heat combustion gas can be supplied to anterior to the lean NOx catalyst via the combustion gas introducing passageway. Accordingly, even after starting up the engine, the combustion gas can be flowed to the exhaust passageway according to the necessity, thereby speeding up the activation of the lean NOx catalyst.
In the case of the internal combustion engine having the turbo charger, the pressure in the intake system may be conceived as a pressure at a point positioned more downstream than the portion provided with the compressor of the turbo charger. Further, the pressure in the exhaust system may be conceived as a pressure at a point positioned more downstream than the portion provided with the turbine of the turbo charger and anterior to the lean NOx catalyst. Note that during the operation of the engine in which the EGR passageway performs its original function as the exhaust gas re-circulation device, the EGR passageway is not, as a matter of course, used as the combustion gas introducing passageway. Further, the xe2x80x9ctime when the pressure in the engine intake system becomes above the predetermined valuexe2x80x9d may be in other words xe2x80x9ca time when the differential pressure between the pressure in the engine intake system and the pressure in the engine exhaust system becomes above the predetermined value.xe2x80x9d
According to an eighth aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the first aspect, wherein when making the request for the reproducing process of the lean NOx catalyst, an output of the combustion heater may become larger than an output thereof that was before making the request for the reproducing process of the lean NOx catalyst so as to increase heat of the combustion gas emitted from the combustion heater. For increasing the output of the combustion heater so that a thermal energy augments, the flames produced by the combustion heater may be grown by increasing the quantities of the air or the fuel fed into the combustion heater.
According to a ninth aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the first aspect, wherein the exhaust passageway includes a catalyst bypass pipe bypassing the lean NOx catalyst, and an exhaust gas flow diverging device for diverging a flow of the exhaust gas to the catalyst bypass pipe and to the lean NOx catalyst, the exhaust gas flow diverging device permitting the flow of the exhaust gas to the catalyst bypass pipe if a temperature of the exhaust gas is lower than an activation temperature of the lean NOx catalyst when making the request for the reproducing process of the lean NOx catalyst.
Furthermore, what is preferable as the exhaust gas flow diverging device may be an opening/closing valve for enabling an opening of the catalyst bypass pipe to open and close. Then, a CPU (Central Processing Unit) of an ECU (Engine Control Unit) controls an operation of the opening/closing valve.
According to a tenth aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the ninth aspect, wherein, of connecting points of the catalyst bypass pipe to the engine exhaust passageway which are formed when the catalyst bypass pipe bypasses the lean NOx catalyst, the connecting point positioned upstream may be provided with the exhaust gas flow diverging device, and a connecting point more downstream than the connecting point where the exhaust gas flow diverging device is provided in the engine exhaust passageway may be connected with the combustion gas introducing passageway which leads the combustion gas emitted from the combustion heater toward upstream of the lean NOx catalyst in the engine exhaust passageway at the time of requesting the reproducing process of the lean NOx catalyst. This geometry intends to transfer, without any waste, the heat of the combustion gas flowing to the exhaust passageway along the combustion gas introducing passageway, to the catalyst.
In the internal combustion engine having the lean NOx catalyst according to the present invention, the exhaust passageway includes the catalyst bypass pipe which bypasses the lean NOx catalyst. The exhaust gas flow diverging device diverges the flow of the exhaust gas toward the catalyst bypass pipe and toward the lean NOx catalyst in the exhaust pipe.
As for this flow-divergence, the exhaust gas is allowed to flow to the catalyst bypass pipe in such a case that the temperature of the exhaust gas is lower than the activation temperature of the lean NOx catalyst when making the request for the reproducing process of the lean NOx catalyst. That is, in the case of the low temperature of the exhaust gas, the exhaust gas flow diverging device cuts off the flow of the exhaust gas toward the lean NOx catalyst but permits the flow thereof toward the catalyst bypass pipe. Hence, only the high-heat combustion gas can be flowed to the lean NOx catalyst via the combustion gas introducing passageway.
With this structure, even when the temperature of the exhaust gas is low, this low-temperature exhaust gas can be prevented from flowing into the lean NOx catalyst. Hence, it never occurs that the temperature of the lean NOx catalyst is decreased by the low-temperature exhaust gas. As a result, the lean NOx catalyst can be easily activated. Further, the catalyst temperature can be sufficiently raised up to the temperature enough to burn the SOF and the particulate matters at a high efficiency, and hence there can be well done the NOx reduction of the lean NOx catalyst, recovery from the S-poisoning or from the SOF-poisoning, and also removal of the particulate matters.
According to an eleventh aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the first aspect, wherein the exhaust passageway may include at least two or more of the lean NOx catalysts, disposed in parallel to one another in a longitudinal direction of the exhaust passageway, to which the flow of the exhaust gas diverges alternately, and an exhaust gas flow diverging device for diverging the flow of the exhaust gas to the lean NOx catalysts. It is preferable that the exhaust gas flow diverging device cuts off the flow of the exhaust gas to the lean NOx catalyst which is in a state of requiring the reproducing process, among those lean NOx catalysts. Note that one end of the combustion gas introducing passageway may branch off in the form of duplex passageways each provided with an opening/closing valve, and may be connected with each lean NOx catalyst via this opening/closing valve.
Further, if none of the plurality of lean NOx catalysts requires the reproducing process, the exhaust gas is not flowed simultaneously to the plurality of lean NOx catalysts but that the exhaust gas is, in the case of, e.g., providing two lean NOx catalysts, flowed to only one catalyst by operating the exhaust gas flow diverging device but is not flowed to the other catalyst until the above-mentioned one catalyst comes to a state of requiring the reproducing process. Then, when one catalyst becomes the state of making the request for the reproducing process, the exhaust gas flow diverging device is operated reversely to the previous operation this time, thereby flowing the exhaust gas to only the other catalyst. Subsequently, at that time, in one catalyst converter, the combustion gas heat is transferred by opening the opening/closing valve related to one catalyst converter, and the reproducing process of one catalyst converter is carried out. At this time, the opening/closing valve related to the other catalyst converter is kept closed.
Next, when the other catalyst converter becomes the state of making the request for reproducing process, the exhaust gas flow diverging device is operated, thereby preventing the exhaust gas from flowing to the other catalyst converter. Simultaneously, the exhaust gas is flowed to only one catalyst converter which has already done the process, and the combustion gas heat is transferred to the other catalyst converter by opening the opening/closing valve related to the other catalyst converter, and the reproducing process of the other catalyst converter is executed.
Thus, of the plurality of catalyst converters, the catalyst converter having come to the state of making the request for the reproducing process is set to non-operating, i.e., does not receive the inflow of the exhaust gas, while the other catalyst converter purifies the exhaust gas, and hence the exhaust gas purifying process can be done with no interruption. It is therefore feasible to carry out the emission and purify the exhaust gas at a high efficiency.
According to a twelfth aspect of the invention, in the internal combustion engine having the lean NOx catalyst according to the first aspect, wherein the combustion heater may allow the flow of the combustion gas through the engine intake passageway.
These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.